1. Field of the Invention
The invention concerns a process and apparatus to control the cooking process in a steam pressure cooker heated by a heating element controlled by a control circuit, wherein the temperature in or on the steam pressure cooker is detected and utilized by the control circuit to regulate the heat output of the heating element, and in which a cooking time is preset by means of an adjustable timing element.
2. Description of the Prior Art
Devices of this kind are known, in which the timing element is manually adjustable and electrically and mechanically separate from the control circuit of the heating element. When the preset cooking time expires, an optical and/or acoustical signal is emitted by the timing element to indicate the end of the cooking time. The heating element is then turned off by hand, and many possible sources of error may effect the cooking time.
In these known devices the cooking time is preset to a fixed time period which disregards the time constant of the cooking system comprising the heating element and steam pressure cooker. Depending upon the size of the steam pressure cooker, the heat output of the heating element, and the amount of cooking material in the pressure cooker, the cooking system has different heating and cooling phases which result in various temperature-time characteristic lines during the cooking process. In addition to the inadequacies of manually shutting off the heating element, consideration of the varying time constants of the cooking system is neglected in the known devices. The cooking time preset by means of the timing element can, however, be so influenced by these variable properties of the cooking system that the cooking time can be too short or too long. In the heating phase, measurement of the cooking time is independent of the actual slope of the temperature-time characteristic line, which can lead to shortening of the actual cooking time. In the cooling phase, after the heating element is shut off, the cooking system remains for some time at the cooking temperature, so that the preset cooking time is lengthened.
In these known devices a further shortcoming appears, since the cooking time also depends on the time constants of the cooking system, which depend on the nature of the cooking material and the amount of cooking material. If, for example, a soup or a vegetable stew or the like is being cooked, then the conditions are different from those in the steaming of potatoes, meat or the like over a waterbath. These types of cooking are hereinafter referred to, respectively, as the cooking of "liquid" or "solid" material. These different types of cooking are also referred to as "cooking" ("boiling" ) or "steaming", respectively.